diff --git a/crates/engine/src/commands/project_items.rs b/crates/engine/src/commands/project_items.rs
index a3949896..197c11a0 100644
--- a/crates/engine/src/commands/project_items.rs
+++ b/crates/engine/src/commands/project_items.rs
@@ -5,7 +5,7 @@ use effectcraft_project::{ItemId, Project};
 use serde_json::{Value, json};
 
 use super::{CommandSpec, always, b_p, bad, str_p};
-use crate::{EngineError, Result, Session, cmd};
+use crate::{EngineError, Result, Session, cmd, query};
 
 /// `item` (id or name) → id.
 fn item_ref(s: &Session, v: &Value, cmd: &str) -> Result<ItemId> {
@@ -140,17 +140,40 @@ fn set_comment(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(Value::Null)
 }
 
+/// The items deleting `ids` removes: them and, for folders, everything inside.
+fn doomed_items(project: &Project, ids: &[ItemId]) -> Vec<ItemId> {
+    project.items.keys().copied().filter(|id| ids.iter().any(|d| is_within(project, *id, *d))).collect()
+}
+
+/// What deleting `items` takes with it: (layers using them, in how many comps), counting only
+/// the comps that stay.
+fn usage_of(project: &Project, items: &[ItemId]) -> (usize, usize) {
+    let mut layers = 0;
+    let mut comps = 0;
+    for (_, comp) in project.comps().filter(|(cid, _)| !items.contains(cid)) {
+        let n = comp.layers.iter().filter(|l| l.source.item().is_some_and(|i| items.contains(&i))).count();
+        layers += n;
+        comps += usize::from(n > 0);
+    }
+    (layers, comps)
+}
+
+/// What deleting the items (default: selected) would delete: the items (with folder contents)
+/// and the layers in other compositions that use them. The Project panel asks before deleting
+/// items in use, as After Effects does.
+fn usage(s: &mut Session, p: &Value) -> Result<Value> {
+    let ids = items_p(s, p, "project.usage")?;
+    let doomed = doomed_items(&s.project, &ids);
+    let (layers, comps) = usage_of(&s.project, &doomed);
+    Ok(json!({"items": doomed.len(), "layers": layers, "comps": comps}))
+}
+
 /// Delete project items (folders with their contents). Layers that use a deleted item and Render
 /// Queue items of deleted comps go too, like After Effects' Edit ▸ Clear in the Project panel.
 fn delete(s: &mut Session, p: &Value) -> Result<Value> {
     let c = "project.delete";
     let ids = items_p(s, p, c)?;
-    let mut doomed: Vec<ItemId> = vec![];
-    for id in s.project.items.keys() {
-        if ids.iter().any(|d| is_within(&s.project, *id, *d)) {
-            doomed.push(*id);
-        }
-    }
+    let doomed = doomed_items(&s.project, &ids);
     let n = doomed.len();
     s.edit("Delete Items", None, |proj, st| {
         for id in &doomed {
@@ -242,6 +265,7 @@ pub fn specs() -> Vec<CommandSpec> {
             always,
             delete
         ),
+        query!("project.usage", "Project Item Usage", "{items?: [id|name] (default: selected)} → {items, layers, comps} that deleting them removes", usage),
         cmd!("project.duplicate", "Duplicate Project Items", [], None, "{items?: [id|name] (default: selected)} → {items}", always, duplicate),
     ]
 }
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 63d1db37..eb2aa1b7 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -84,6 +84,8 @@ pub enum Dialog {
     RenderTemplates,
     /// Save changes before closing the project? (`panels::unsaved`).
     UnsavedChanges,
+    /// Delete Project items that compositions use? (`panels::delete_items`).
+    DeleteItems,
 }
 
 /// Host hooks provided by the native app (file pickers etc.).
diff --git a/crates/ui-egui/src/menus.rs b/crates/ui-egui/src/menus.rs
index c83bb03f..0c2e7dec 100644
--- a/crates/ui-egui/src/menus.rs
+++ b/crates/ui-egui/src/menus.rs
@@ -196,6 +196,10 @@ pub fn invoke(app: &mut EffectcraftApp, ctx: &egui::Context, id: &str, params: V
     if crate::panels::unsaved::guard(app, id, &params) {
         return Ok(json!({"dialog": "unsavedChanges"}));
     }
+    // Deleting Project items that compositions use asks first, as in After Effects.
+    if crate::panels::delete_items::guard(app, id, &params) {
+        return Ok(json!({"dialog": "deleteItems"}));
+    }
     // J / K and Select All Keyframes act on what the Timeline shows (its revealed properties).
     if matches!(id, "time.nextKey" | "time.previousKey" | "keys.selectAll")
         && ["visible", "layers", "layer", "prop"].iter().all(|k| params.get(*k).is_none())
diff --git a/crates/ui-egui/src/panels/delete_items.rs b/crates/ui-egui/src/panels/delete_items.rs
new file mode 100644
index 00000000..dbda93d7
--- /dev/null
+++ b/crates/ui-egui/src/panels/delete_items.rs
@@ -0,0 +1,86 @@
+//! Deleting Project items that compositions use asks first, as in After Effects: the Delete key
+//! and the Project panel's trash button (`project.delete` through the UI) show how many layers in
+//! how many compositions go with the items (`project.usage`). Items nothing uses are deleted at
+//! once. Agents running `project.delete` with `engine.execute` are never asked.
+//!
+//! Automation ids: `dialog.deleteItems.delete`, `dialog.deleteItems.cancel`.
+
+use egui::{Color32, vec2};
+use serde_json::Value;
+
+use crate::theme::Tokens;
+use crate::{Dialog, EffectcraftApp};
+
+/// The deletion waiting on the prompt: its params and what it takes with it.
+#[derive(Clone, Debug, Default)]
+pub struct Pending {
+    pub command: Option<(Value, Value)>,
+    /// The next `project.delete` runs without asking (the user answered Delete).
+    pub answered: bool,
+}
+
+fn plural(n: u64, one: &str, many: &str) -> String {
+    format!("{n} {}", if n == 1 { one } else { many })
+}
+
+/// Whether `id` needs the prompt first. When it does, the prompt opens holding the command and
+/// the caller must not run it (it runs once the user answers Delete).
+pub fn guard(app: &mut EffectcraftApp, id: &str, params: &Value) -> bool {
+    if id != "project.delete" || std::mem::take(&mut app.dialog_state.delete_items.answered) {
+        return false;
+    }
+    let Ok(usage) = app.session.execute("project.usage", params.clone()) else { return false };
+    if usage["layers"].as_u64().unwrap_or(0) == 0 {
+        return false;
+    }
+    app.dialog_state.delete_items.command = Some((params.clone(), usage));
+    app.dialog = Some(Dialog::DeleteItems);
+    true
+}
+
+pub fn show(app: &mut EffectcraftApp, ctx: &egui::Context, t: &Tokens) {
+    let Some((params, usage)) = app.dialog_state.delete_items.command.clone() else {
+        app.dialog = None;
+        return;
+    };
+    let n = |k: &str| usage[k].as_u64().unwrap_or(0);
+    let mut answer: Option<bool> = None;
+    super::dialogs::modal(ctx, "Delete Items", vec2(460.0, 160.0), t, |ui| {
+        let text = format!(
+            "Delete {}? {} in {} {} {} and will be deleted too.",
+            plural(n("items"), "item", "items"),
+            plural(n("layers"), "layer", "layers"),
+            plural(n("comps"), "composition", "compositions"),
+            if n("layers") == 1 { "uses" } else { "use" },
+            if n("items") == 1 { "it" } else { "them" },
+        );
+        ui.label(egui::RichText::new(text).color(t.tab_text_active));
+        ui.add_space(4.0);
+        ui.label(egui::RichText::new("You can undo this.").color(t.text_dim).size(11.0));
+        ui.add_space(18.0);
+        ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
+            let r = ui.add(egui::Button::new(egui::RichText::new("  Delete  ").color(Color32::WHITE)).fill(t.danger));
+            app.auto.add("dialog.deleteItems.delete", r.rect, "Delete");
+            if r.clicked() {
+                answer = Some(true);
+            }
+            let r = ui.button("Cancel");
+            app.auto.add("dialog.deleteItems.cancel", r.rect, "Cancel");
+            if r.clicked() {
+                answer = Some(false);
+            }
+        });
+    });
+    if answer.is_none() && ctx.input(|i| i.key_pressed(egui::Key::Escape)) {
+        answer = Some(false);
+    }
+    let Some(delete) = answer else { return };
+    app.dialog = None;
+    app.dialog_state.delete_items.command = None;
+    if delete {
+        app.dialog_state.delete_items.answered = true;
+        if let Err(e) = crate::menus::invoke(app, ctx, "project.delete", params) {
+            app.ui.status = e;
+        }
+    }
+}
diff --git a/crates/ui-egui/src/panels/dialogs.rs b/crates/ui-egui/src/panels/dialogs.rs
index d806827c..5832d2c8 100644
--- a/crates/ui-egui/src/panels/dialogs.rs
+++ b/crates/ui-egui/src/panels/dialogs.rs
@@ -57,6 +57,8 @@ pub struct DialogState {
     pub layer_style: super::layer_styles_dialog::LayerStyleState,
     /// The unsaved-changes prompt and the command it holds.
     pub unsaved: super::unsaved::Pending,
+    /// Deleting Project items in use: the deletion waiting on the prompt.
+    pub delete_items: super::delete_items::Pending,
 }
 
 pub fn open_new_comp(app: &mut EffectcraftApp) {
@@ -188,6 +190,7 @@ pub fn show(app: &mut EffectcraftApp, ctx: &egui::Context) {
         Dialog::TrackApply => super::tracker::apply_dialog(app, ctx, &t),
         Dialog::RenderTemplates => super::rq_templates::show(app, ctx, &t),
         Dialog::UnsavedChanges => super::unsaved::show(app, ctx, &t),
+        Dialog::DeleteItems => super::delete_items::show(app, ctx, &t),
     }
 }
 
diff --git a/crates/ui-egui/src/panels/mod.rs b/crates/ui-egui/src/panels/mod.rs
index 0021c159..c7484859 100644
--- a/crates/ui-egui/src/panels/mod.rs
+++ b/crates/ui-egui/src/panels/mod.rs
@@ -4,6 +4,7 @@ pub mod anim_tools;
 pub mod camera_tracker_ui;
 pub mod comp_settings;
 pub mod content_fill_panel;
+pub mod delete_items;
 pub mod dialogs;
 pub mod dialogs_3d;
 pub mod effect_controls;
diff --git a/crates/ui-egui/tests/ui_project_delete.rs b/crates/ui-egui/tests/ui_project_delete.rs
index a343740d..97f12d86 100644
--- a/crates/ui-egui/tests/ui_project_delete.rs
+++ b/crates/ui-egui/tests/ui_project_delete.rs
@@ -2,8 +2,8 @@
 
 use effectcraft_engine::Session;
 use effectcraft_engine::project::{Footage, FootageKind, ItemId, ItemKind, LayerId};
-use effectcraft_ui_egui::EffectcraftApp;
 use effectcraft_ui_egui::dock::PanelKind;
+use effectcraft_ui_egui::{Dialog, EffectcraftApp};
 use egui::{Event, Key, Modifiers, pos2};
 use egui_kittest::Harness;
 use serde_json::json;
@@ -48,6 +48,16 @@ fn key(h: &mut Harness<'_, EffectcraftApp>, key: Key, modifiers: Modifiers) {
     h.run_steps(2);
 }
 
+/// Items that compositions use ask first, as in After Effects: answer Delete when asked.
+/// Returns whether it asked.
+fn confirm_if_asked(h: &mut Harness<'_, EffectcraftApp>) -> bool {
+    if h.state().dialog != Some(Dialog::DeleteItems) {
+        return false;
+    }
+    click(h, "dialog.deleteItems.delete", Modifiers::NONE);
+    true
+}
+
 #[test]
 fn delete_and_backspace_remove_project_items_and_undo() {
     for delete_key in [Key::Delete, Key::Backspace] {
@@ -61,6 +71,8 @@ fn delete_and_backspace_remove_project_items_and_undo() {
             let project = h.state().session.project.clone();
             let undo = h.state().session.history.undo.len();
             key(&mut h, delete_key, Modifiers::NONE);
+            // Only the solid is used by a layer: only it asks first.
+            assert_eq!(confirm_if_asked(&mut h), target == 1, "item {target}");
             assert!(h.state().session.project.item(item).is_none(), "{delete_key:?} should delete project item {target}");
             assert!(h.state().session.active_comp().unwrap().layer(keep).is_some(), "the unrelated Timeline layer stays");
             assert!(h.state().session.state.project_selection.is_empty());
@@ -82,6 +94,7 @@ fn project_multi_selection_deletes_together_and_undoes_once() {
     let project = h.state().session.project.clone();
     let undo = h.state().session.history.undo.len();
     key(&mut h, Key::Backspace, Modifiers::NONE);
+    assert!(confirm_if_asked(&mut h), "the solid is in use");
     assert!(items.iter().all(|i| h.state().session.project.item(*i).is_none()));
     assert!(h.state().session.active_comp().unwrap().layer(keep).is_some());
     assert_eq!(h.state().session.history.undo.len(), undo + 1);
@@ -139,3 +152,38 @@ fn typing_dialogs_and_modified_keys_do_not_delete_project_items() {
         assert_eq!(h.state().session.project, project, "typing must not delete the item");
     }
 }
+
+/// Deleting an item a composition uses asks first, as in After Effects, and says what goes with
+/// it; Cancel and Escape keep everything, Delete removes the item and the layers using it in one
+/// undo step. Agents running the command directly are not asked.
+#[test]
+fn deleting_items_in_use_asks_first() {
+    let (mut h, items, _) = harness();
+    let solid = items[1];
+    let usage = h.state_mut().session.execute("project.usage", json!({"items": [solid.0]})).unwrap();
+    assert_eq!(usage, json!({"items": 1, "layers": 1, "comps": 1}));
+    let uses = |h: &Harness<'_, EffectcraftApp>| {
+        h.state().session.project.comps().flat_map(|(_, c)| c.layers.iter()).filter(|l| l.source.item() == Some(solid)).count()
+    };
+    click(&mut h, &format!("project.item.{}.name", solid.0), Modifiers::NONE);
+    for cancel in ["button", "escape"] {
+        key(&mut h, Key::Delete, Modifiers::NONE);
+        assert_eq!(h.state().dialog, Some(Dialog::DeleteItems));
+        if cancel == "button" {
+            click(&mut h, "dialog.deleteItems.cancel", Modifiers::NONE);
+        } else {
+            key(&mut h, Key::Escape, Modifiers::NONE);
+        }
+        assert_eq!(h.state().dialog, None, "{cancel}");
+        assert!(h.state().session.project.item(solid).is_some() && uses(&h) == 1, "{cancel} keeps the item and its layer");
+    }
+    let undo = h.state().session.history.undo.len();
+    key(&mut h, Key::Delete, Modifiers::NONE);
+    assert!(confirm_if_asked(&mut h));
+    assert!(h.state().session.project.item(solid).is_none() && uses(&h) == 0);
+    assert_eq!(h.state().session.history.undo.len(), undo + 1);
+    // The command itself (agents, scripts) deletes without asking.
+    h.state_mut().session.execute("edit.undo", json!({})).unwrap();
+    h.state_mut().session.execute("project.delete", json!({"items": [solid.0]})).unwrap();
+    assert!(h.state().session.project.item(solid).is_none());
+}